(NaturalNews) The obesity epidemic appears to be expanding beyond humankind and into the animal kingdom, according to a new report out of the University of Alabama, Birmingham (UAB). David Allison, the UAB researcher who led the study, discovered that animals in general have been getting progressively larger -- even in controlled settings -- which has led to more questions than answers as to why this phenomenon is occurring.

While poring over data on marmosets at the Wisconsin National Primate Researcher Center, Allison came to discover that this species of monkey has been gaining weight throughout the decades, even though nothing much has changed in terms of their rearing. In fact, one of the only significant changes was the marmosets' diet which, according to experts, should have caused the animals to lose weight, if anything.

Published in the journal Proceedings of the Royal Society B, Allison's study revealed that many other animals -- including laboratory, domestic, and feral ones -- have all been getting progressively larger over time. After grouping the animals into 24 different categories of species and sexes, Allison discovered that literally every single one of them has been growing increasingly obese.

"We can't explain the changes in [the animals'] body weight by the fact that they eat out at restaurants more often or the fact that they get less physical education in the schools," explained Allison to LiveScience. "There can be other factors beyond what we obviously reach for."

Though researchers say they are at a loss for answers, others suspect that chemical food additives and genetic modification of food both play a role in rising obesity levels. A 2009 study out of the Mount Sinai School of Medicine found that phthalate chemicals used in food packaging are linked to childhood obesity (http://www.naturalnews.com/026427_studies_na...). And an earlier study found that babies exposed to common chemicals in utero are twice as likely to become obese (http://www.naturalnews.com/024328_chemicals_...).